Sublethal hypoxic injury increases intestinal permeability via disruption of sealing tight junction proteins, but not pore forming tight junction proteins in human intestinal epithelium

Intestinal ischemia induces loss of barrier function which is followed by epithelial repair. The tight junction (TJ) has recently been characterized as having both leak and pore properties. We hypothesized that hypoxia would disrupt the TJ seal prior to the pore function followed by barrier recovery. Caco‐2 BBe1 confluent monolayers were subjected to hypoxia for 2 hours followed by recovery in 21% O 2 , after which barrier function was determined by measuring transepithelial electrical resistance (TER) and flux of 4 kDa FITC‐dextran. TJ proteins were studied by immunoblotting and immunolocalization. Following hypoxic injury, there was an increase in the paracellular permeability, as determined by dextran fluxes, but no change in TER compared to control cells. Permeability recovered with significant reduction in fluxes at 2 and 4 h. The sealing TJ proteins occludin and claudin‐4 increased expression after hypoxic injury. However, the occludin and claudin‐4 fluorescence was diffuse on confocal microscopy, but re‐localized their normal distribution after 4 h recovery. The expression and distribution of the pore forming TJ protein claudin‐7 was not changed. This correlated with a lack of change in TER. These data suggest that hypoxic injury increases paracellular permeability by disruption of sealing TJ proteins, creating a leak but not altering pore selectivity.